1. Field of the Invention
This invention relates to an apparatus and method for separating various materials. In particular, this invention relates to improvements in a unique disc screen that improves the screen's performance and reduces maintenance thereof.
2. Description of the Related Art
Disc or roll screens, as contemplated by the present invention are frequently used as part of a multi-stage materials separating system. Disc screens are used in the materials handling industry for screening large flows of materials to remove certain items of desired dimensions. In particular, disc screens are particularly suitable for classifying what is normally considered debris or residual materials. This debris may consist of various constituents. It may contain soil, aggregate, asphalt, concrete, wood, biomass, ferrous and nonferrous metal, plastic, ceramic, paper, cardboard, or other products or materials recognized as debris throughout consumer, commercial and industrial markets. The function of the disc screen is to separate the materials fed into it by size. The size classification may be adjusted to meet virtually any specific application.
Disc screens generally have a screening bed having a series of rotating spaced parallel shafts each of which has a longitudinal series of concentric screen discs separated by spacers which interdigitate with the screen discs of the adjacent shafts. The relationship of the discs and spacers on one shaft to the discs and spacers on each adjacent shaft form an opening generally known in the industry as the interfacial opening or "IFO". The IFOs permit only material of acceptable size to pass downwardly through the rotating disc bed. The acceptable sized material which drops through the IFO is commonly referred to in the industry as Accepts or Unders.
The discs are all driven to rotate in a common direction from the infeed end of the screen bed to the outfeed or discharge end of the bed. Thus, materials which are larger than the IFO, referred to in the industry as Overs, will be advanced on the bed to the outfeed end of the bed and rejected.
A major problem with such disc screens is jamming. When the discs are not in line, material tends to jam between the disc and the adjacent shaft, physically forcing the screen to stop. Although the jamming phenomenon may not cause the roll screen to stop completely, it may cause momentary stoppages. Such stoppages may not cause the drive mechanism of the roll screen to turn off but may cause substantial mechanical shock. This mechanical shock eventually results in the premature failure of the roll screen's roll assemblies and drive mechanism.
Another problem with disc screens is effectively separating debris having similar shapes. It is difficult to separate office sized waste paper (OWP) and old newspapers (ONP) since much of the OWP and ONP has the same long thin shape. For example, it is difficult to effectively separate notebook paper and ONP from old corrugated cardboard (OCC) since each is long and relatively flat. A secondary slot is formed between the discs on adjacent shafts. OWP and/or OCC is difficult to sort effectively because most categories of OWP and some OCC can slip through the secondary slot. Further, OWP has a tendency to slip off a bottom end of the disc screen, while being transported up the screen at an incline.
Accordingly, a need remains for a system that can classify materials more effectively and is also more resistant to jamming.